In-Plane MEMS Optical Switch

ABSTRACT

An optical switch includes a first bus waveguide supported by a substrate, an optical antenna suspended over the first bus waveguide via a spring, and interdigitated electrodes coupling the substrate with optical antenna and configured to control a position of the optical antenna relative to the first bus waveguide. When a voltage difference applied to the interdigitated electrodes is less than a lower threshold, the optical antenna is at a first position offset from the first bus waveguide, when the voltage difference applied to the interdigitated electrodes is greater than an upper threshold, the optical antenna is at a second position offset from the first bus waveguide, and the offset at the second position is greater than at the first position.

CROSS-REFERENCE TO RELATED APPLICATIONS Technical Field

This invention relates generally to a system and apparatus forchanneling and emitting light signals.

BACKGROUND

Lidar is considered to be a key enabler for many new technologies suchas autonomous vehicles. Chip-Lidar (also known as solid-state Lidar, orLidar on a chip) is expected to be widely used in future autonomousvehicles. However, many challenges remain in creating a practicalchip-Lidar that can meet the requirements of vehicle OEMs. One of thechallenges is beam steering. There has been various approaches developedto steer a beam in chip-Lidar, such as micro mirror array, opticalphased array, wavelength tuning, and photonic crystal waveguides,however, these approaches face challenges such as limited field of view,complicated control electronics, and high requirement of the laser.

SUMMARY

An optical switch includes a first bus waveguide supported by asubstrate, an optical antenna suspended over the first bus waveguide viaa spring, and interdigitated electrodes coupling the substrate withoptical antenna and configured to control a position of the opticalantenna relative to the first bus waveguide. When a voltage differenceapplied to the interdigitated electrodes is less than a lower threshold,the optical antenna is at a first position offset from the first buswaveguide, when the voltage difference applied to the interdigitatedelectrodes is greater than an upper threshold, the optical antenna is ata second position offset from the first bus waveguide, and the offset atthe second position is greater than at the first position.

An optical switch includes a bus waveguide supported by a substrate, anoptical antenna suspended over the bus waveguide via a spring, andinterdigitated electrodes coupling the substrate with optical antennaand configured to control a position of the optical antenna relative tothe bus waveguide. When a voltage difference applied to theinterdigitated electrodes is less than a lower threshold, the opticalantenna is disposed at a first position relative to the bus waveguide,when the voltage difference applied to the interdigitated electrodes isgreater than an upper threshold, the optical antenna is disposed at asecond position relative to the bus waveguide, and the first position isseparated from the second position by a predetermined distance.

A beam steering system includes a bus waveguide supported by asubstrate, an optical antenna supported a distance over the buswaveguide via a spring, interdigitated electrodes that couple thesubstrate to the optical antenna and are configured to control aposition of the optical antenna relative to the bus waveguide, anoptical tree and a lens. The optical tree has at least one type ofoptical switch, the optical tree configured to collect light from theoptical antenna. The lens is spaced apart from the substrate andconfigured to diffract the light onto the optical antenna. When avoltage difference applied to the interdigitated electrodes is less thana lower threshold, the optical antenna is positioned a first distanceoffset from the bus waveguide, when the voltage difference applied tothe interdigitated electrodes is greater than an upper threshold, theoptical antenna is positioned a second distance offset from the buswaveguide, and the second distance is less than the first distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an optical switch array system.

FIG. 2 is a side view of an optical switch array system.

FIG. 3 is a perspective view of a silicon photonic switch array.

FIG. 4A is a top view of an optical switch of an optical switch array.

FIG. 4B is a side view of an optical switch of an optical switch arrayin an OFF state.

FIG. 4C is a side view of an optical switch of an optical switch arrayin an ON state.

FIG. 5A is a perspective view of an optical switch with an opticalcoupled cantilever and fixed optical antenna in a switch array.

FIG. 5B is a perspective view of a 2 dimensional fixed optical antenna.

FIG. 6 is a perspective view of an optical coupled cantilever with afixed optical antenna.

FIG. 7A is a cut view of the optical coupled cantilever of the MEMSswitch of FIG. 6 in an idle state.

FIG. 7B is a cut view of the optical coupled cantilever of the MEMSswitch of FIG. 6 in an actuated state.

FIG. 7C is a cut view of the fixed optical antenna of the MEMS switch ofFIG. 6 in an idle state.

FIG. 7D is a cut view of the fixed optical antenna of the MEMS switch ofFIG. 6 in an actuated state.

FIG. 8 is a perspective view of an optical switch array systemtransmitting an optical signal.

FIG. 9 is a perspective view of an optical switch array system receivingan optical signal.

FIG. 10 is a perspective view of an optical switch array systemreceiving and transmitting optical signals.

FIG. 11 is a perspective view of an optical switch array systemincluding at least two types of optical switches.

FIG. 12 is a perspective view of an optical switch array systemincluding a splitter tree and an optical switch.

FIG. 13 is a perspective view of an optical switch array systemincluding a splitter tree and at least two types of optical switches.

FIG. 14 is a diagram of a switch array system configured toindependently address rows and columns.

FIG. 15 is a diagram of a switch array system configured to address subarrays simultaneously.

FIG. 16 is a perspective view of a bus waveguide and a correspondingcoupler waveguide.

FIG. 17 is a graphical representation of coupling field profile withrespect to distance.

FIG. 18 is a series of 2-dimension graphical representations of couplingfield profiles with respect to propagation distance.

FIG. 19 is a graphical representation of coupling efficiency withrespect to coupling taper length.

FIG. 20 is a graphical representation of transmission loss with respectto wavelength.

FIG. 21 is a graphical representation of energy loss with respect to gapsize.

FIG. 22 is a graphical representation of a radiation pattern withrespect to angle.

FIG. 23 is a side view illustration of a waveguide grating to free spaceangle.

FIG. 24 is a perspective view of a cantilever spring biased by avoltage.

FIG. 25 is a graphical representation of displacement along a Z-axiswith respect to switching speed.

FIG. 26 is a top view of a switch array layout with a detailedillustration of a single element.

FIG. 27A is a perspective view of a switch array with movable opticalcoupler on a suspension layer and a fixed optical antenna on a substratelayer.

FIG. 27B is a top view of a switch array with movable optical coupler ona suspension layer and a fixed optical antenna on a substrate layer.

FIG. 28A is a cross sectional view of the movable optical coupler ofFIG. 27 while in the OFF position.

FIG. 28B is a cross sectional view of the movable optical coupler ofFIG. 27 while in the ON position.

FIG. 29 is a top view of a switch array layout with a movable opticalcoupler on a suspension layer and a fixed optical antenna on a substratelayer with a detailed illustration of a single element.

FIG. 30 is a top view of a switch array layout with a movable opticalcoupler on a suspension layer and a fixed optical antenna on a substratelayer with a detailed illustration of a single element.

FIG. 31 is a top view of an element of a switch array layout with amovable optical coupler on a suspension layer and a fixed opticalantenna on a substrate layer.

FIG. 32 is a cross sectional view of the element of FIG. 31.

FIG. 33 is a graphical representation of a field profile of a gratingantenna with respect to X and Y coordinates.

FIG. 34 is a perspective view of a illustrating displacement of anoptical coupler.

FIG. 35 is a perspective view of a grating antenna illustrating emissionangles.

FIG. 36 is a graphical representation of intensity with respect toemission angles.

FIG. 39 is a side view illustrating a mirror to compensate for anon-zero antenna emission angle.

FIG. 40 is a side view illustrating an optical prism to compensate for anon-zero antenna emission angle.

FIG. 41 is a side view illustrating a micro-prism array to compensatefor non-zero antenna emission angle.

FIG. 42A is a top view of an antenna array with splitter trees andswitches.

FIG. 42B is a top view of an antenna array with multiple switch types.

FIG. 42C is a top view of an antenna array with splitter trees andmultiple switch types.

FIG. 43A is a perspective view of a switch array with a moveable gratingthat travels longitudinally with multiple stop positions.

FIG. 43B is a perspective detailed view of a moveable grating thattravels longitudinally with multiple stop positions to the bus waveguidefrom FIG. 43A.

FIG. 43C is a perspective view of a switch array with a moveable gratingthat travels longitudinally to the bus waveguide.

FIG. 43D is a perspective detailed view of two moveable gratings thattravel longitudinally to the bus waveguide from FIG. 43C.

FIG. 43E is a top view of a movable grating that travels longitudinallyto the bus waveguide via interdigitated electrodes.

FIG. 44A is a perspective view of a switch array with a moveable gratingthat travels transversely to the bus waveguide with multiple stoppositions.

FIG. 44B is a perspective detailed view of a moveable grating thattravels transversely to the bus waveguide with multiple stop positionsof the switch array from FIG. 43A.

FIG. 44C is a top view of a movable grating that travels transversely tothe bus waveguide via interdigitated electrodes.

FIG. 45 is a perspective view of a switch array with a moveable gratingthat travels transversely with stop positions in-plane and off-planewith waveguides.

FIG. 46 is a perspective view of a switch with electrostatic levitationto control a coupling distance between a bus waveguide and the gratings.

FIG. 47A is a perspective view of a switch with a comb drive to controla coupling distance between a bus waveguide and the gratings.

FIG. 47B is a cross-sectional view along a cut of FIG. 47A illustratingthe comb drive.

FIG. 48 is a cross-sectional view of a switch array system illustratingpackaging.

FIG. 49 is a perspective view of a dual grating switch that travelstransversely with stop positions in-plane with waveguides.

FIG. 50 is a perspective view of a dual grating switch that travelstransversely with stop positions in-plane and off-plane with waveguides.

FIG. 51 is a perspective view of a bimorphic switch in which a gratingis an in-plane position.

FIG. 52 is a perspective view of a bimorphic switch that rotates agrating vertically in an off-plane position.

FIG. 53 is a perspective view of switch array in which grating elementsrotate about an axis perpendicular with the wave guide.

FIG. 54 is a perspective view of switch array in which grating elementsrotate about an axis parallel with the wave guide.

FIG. 55 is a top view of a grating array on a rotary platter thatutilizes a rotational mechanism to align in-plane and off-planeoperation.

FIG. 56A is a cross sectional view of a coupler waveguide with abi-stable membrane in an OFF position.

FIG. 56B is a cross sectional view of a coupler waveguide with abi-stable membrane in an ON position.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

The term “substantially” may be used herein to describe disclosed orclaimed embodiments. The term “substantially” may modify a value orrelative characteristic disclosed or claimed in the present disclosure.In such instances, “substantially” may signify that the value orrelative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%,3%, 4%, 5% or 10% of the value or relative characteristic.

Although in this application different embodiments are illustrated withthe use of silicon MEMS structures, the MEMS structures may be otherMEMS material such as SiC, SiN,

This disclosure presents microelectromechanical system (MEMS) switches,switch arrays, and systems including MEMS switches with couplercantilever and multiple fixed optical antenna configurations. Such MEMSswitches can be used to couple light from a waveguide on photonicintegrated circuit (PIC) chip to free space in various applications.

Lidar is a key enabler for many new systems such as autonomous driving.Chip-Lidar (also known as solid-state Lidar, Lidar on a chip) isexpected to be widely used in future autonomous vehicles due to itscompact size and low cost. Nevertheless, many challenges still remain increating a practical chip-Lidar meeting the requirements from OEMs. Oneof the challenges is beam steering. Various approaches have beendeveloped to steer beam in chip-Lidar, such as micro mirror array,optical phased array, wavelength tuning, photonic crystal waveguides,etc. However, these approaches are facing one or more challenges such aslimited field of view, complicated control electronics, high requirementof laser, low technology maturity, etc.

Besides the approaches mentioned above, an optical amplitude array canalso steer optical beam in chip-Lidar. FIG. 1 is a top view of anoptical switch array system 100. The system 100 includes a photonicintegrated circuit (PIC) chip 102, multiple optical sources/opticalantennae 104, and a lens 106. FIG. 2 is a side view of an optical switcharray system 200. The system 200 includes a photonic integrated circuit(PIC) chip 202, multiple optical sources/optical antennae 204, and alens 206.

As shown in FIG. 1 (top view) and FIG. 2 (side view), an opticalamplitude array consists of an array of optical sources or opticalantennas (e.g., 104, 204)(each optical source or optical antenna can beregarded as one “pixel”) and a lens or lens system (e.g., 106, 206)(“lens” is used in the following description for simplicity), with theoptical pixel array locating at the focal plane (or in close proximityto the focal plane) of the lens. The light amplitude emitting from eachoptical pixel can be either 0 (no light emission) or 1 (full lightemission). The emitted light from each optical pixel experiencesrefraction when passing through the lens and is deflected into certaindirection following physical optical laws. By switching on an opticalpixel at different positions, light can be controlled and steered intodifferent directions in free space, and thus beam steering is achieved.A two-dimensional (2D) arranged optical pixel array can realize 2D beamsteering.

There are various ways to make an optical pixel array. For example, suchan array can be made up of an array of optical sources, such asVertical-External-Cavity Surface-Emitting-Laser (VECSELs). Such an arraycan also be composed of a waveguide array with optical antenna armycontrolled by optical switch array. In this disclosure, methods areexplored including optical MEMS switch arrays configured to controllight emission from the optical antennas.

This disclosure includes beam steering enabled by a MEMS switch basedamplitude array. Such MEMS switch based amplitude array consists of awaveguide array with MEMS switchable antennas being located at or inclose proximity to the focal plane of a lens. Switching on opticalantennas at different positions can steer the beam to differentdirections, as shown in FIG. 1 and FIG. 2.

Compared to the micro mirror array based beam steering, the amplitudearray beam steering can reach a larger field-of-view. Compared tooptical phased array beam steering, the amplitude array beam steeringrequires much simpler control electronics. Compared to wavelength tuningbased beam steering, the amplitude array beam steering does not requirelarge wavelength tunability of the laser source. Compared to thephotonic crystal waveguide based beam steering, the amplitude array beamsteering is more straightforward and technically more stable.

There are many options for optical switches. The most common ones thatcan be used in the amplitude array application include micro mirrorbased switches, liquid-crystal switches, thermo-optical switches, etc.The micro mirror based switches and liquid-crystal switches have arelatively large size such as hundreds of micrometers, and requireswitching time in the millisecond range, which makes each pixel toolarge and too slow for the chip-Lidar application. The thermo-opticalswitches, on the other hand, have low extinction ratio and highinsertion loss, which is also not good for this application. MEMSstructure based optical switch can be compact and fast switching andhave high extinction ratio, therefore this technology is a goodcandidate for the amplitude array application.

FIG. 3 is a perspective view of a silicon photonic integrated switch(PIC) array 300. The array has in-ports 310, through ports 314, and dropports 312, such that when a low-loss crossing 316, such as an opticalswitch, is activated the light travels from the in-port 310 to throughthe low-loss crossing 316 to the drop port 312. For the light to travelfrom the in-port 310 to the low-loss crossing 316, a MEMS actuatedadiabatic coupler must be a certain distance from the bus waveguide.When a low-loss crossing 316 is not activated the light travels from thein-port 310 to the through port 314.

A close-up view of an optical switch element of the array 304 includes aMEMS actuated adiabatic coupler 318 and a bus waveguide 320. Anillustration of the optical switch in an off state 306, in which lightpasses from the input 310 to the output 314 while the cantilever coupleris a distance 316 from the bus waveguide such that the couplingefficiency is less than 1%. An illustration of the optical switch in anon state 308, in which light passes from the input 310 to the output 312while the cantilever coupler 318 is activated such that light from thebus waveguide couples with the output 312 with a coupling efficiencygreater than 50%.

As shown in FIG. 3, such a silicon photonic MEMS switch network employstwo orthogonal sets of bus waveguides and MEMS-actuated verticaladiabatic couplers. The vertical gap distance can be controlled by MEMSelectrostatic actuators and the mechanical stoppers. In the OFF state,the adiabatic couplers are located far above the waveguides, so lightcontinues to propagate toward the through port without interruption. Inthe ON state, the adiabatic couplers are moved toward the buswaveguides, and light is coupled to the adiabatic couplers, and thencoupled out to the drop port by another adiabatic coupler.

MEMS switch can be used to selectively couple light in and out of awaveguide in an optical transmit/receive terminal. In one embodiment,each optical switch may be implemented by a physically translatableoptical grating. In the OFF state, the translatable optical grating issufficiently far above the bus waveguide, and in the ON state, MEMSactuators can move the translatable optical grating down towards the buswaveguide for efficient light coupling between the grating and the buswaveguide.

FIG. 4A is a top view of an optical switch 400. The optical switch 400includes a grating 402 that comprises multiple optical coupler elements404, 406, 408 that are aligned with a bus waveguide 410. FIG. 4B is aside view of the optical switch 400 in an OFF state. A wave 412 travelsin a direction 414 in the bus waveguide 410. The bus waveguide issupported by a substrate 416 and in the OFF state, the grating 402 is adistance 418 above the bus waveguide 410 such that the couplingefficiency between the grating 402 and bus waveguide 410 is low and thewave continues to propagate in the bus waveguide 410. FIG. 4C is a sideview of the optical switch 400 in an ON state. In this figures, thegrating 402 is a distance 420 above the bus waveguide 410 such that thecoupling efficiency between the grating 402 and bus waveguide 410 ishigh and the wave refracts 422 into free space from the bus waveguide410.

In this disclosure, multiple MEMS switch embodiments are including aMEMS switch with coupler cantilever and optical antenna. FIG. 5Aillustrates an array of such MEMS switch used in optical terminals. Heregratings are used as an optical antenna in an example to illustrate theconcept, other optical antennas (e.g. FIG. 5B) also work in thisconcept.

FIG. 5A is a perspective view of an optical switch with an opticalcoupled cantilever and fixed optical antenna in a switch array 500. Theswitch array 500 may be on a single substrate 502 or can be configuredas a multi-chip module in which multiple optical switches aremonolithically integrated on a photonic integrated circuit (PIC) chipthat is then combined with other PIC chips to form the array system 500.The single substrate photonic integrated circuit (PIC) chip 502 includesa bus waveguide configured to input light 504 and distribute the lightamong multiple rows 510 and columns of optical switches. Here three rowsare configured as a first row 510 a, a second row 510 b, and a third row510 c in which each row has three columns of optical switches 506.

FIG. 5B is a perspective view of a 2-dimensional fixed optical antenna550. The optical antenna includes a coupler cantilever 552 and anoptical antenna that had a length 554 and width 556. The ratio of length554 to width 556 could be substantially 3:1, 5:2, 2:1, or similar. Witha gap 558 between the optical antenna and side that may be substantially0.2, 0.3, 0.4, 0.5, 0.6 of the width 556. The optical antenna can beconfigured to substantially output or receive light along an angle in ax-axis 560 and along an angle in a y-axis 562.

FIG. 6 is a perspective view of a MEMS switch 600 with an opticalcoupled cantilever 614 and a fixed optical antenna 616. The MEMS switch600 includes a substrate 602 such as a silicon substrate with aninsulating layer 604 such as silicon dioxide. On top of the insulatinglayer 604 are structure layers 606, such as silicon layers. In thestructure layers 606 are structures such as a bus waveguide 608, a MEMSactuation electrode 610, a MEMS spring 612, the coupling cantilever 614,and the optical antenna 616. In this embodiment, the coupling waveguide614 moves or articulates based on MEMS principles. For example, the MEMSactuation electrode 610 could be configured to corporate with a reactionelectrode located adjacent to the coupling waveguide and between theMEMS spring 612 and coupling waveguide 614. When a voltage difference isapplied between the reaction electrode and the actuation electrode thatis less than a lower threshold, the coupling waveguide is held viaelectrostatic forces at a first distance from the bus waveguide. Thelower threshold may be a low differential voltage such as 0 volts orsome low voltage around zero volts such as −5, −4, −3, −2, −1, 1, 2, 34,or 5 volts. A voltage below this lower threshold, the couplingcantilever may either maintain a rest position, or possible slightlymove such that the coupling efficiency between the bus waveguide 608 andthe optical antenna 616 via the coupling waveguide 614 is less than 1%(e.g., turned off). Similarly when the voltage difference between thereaction electrode and the actuation electrode 610 is greater than anupper threshold, the coupling waveguide is held via electrostatic forcesat a second distance from the bus waveguide 608 in which the seconddistance is less than the first distance. For example, at the seconddistance, the coupling efficiency between the bus waveguide 608 and theoptical antenna 616 via the coupling waveguide 614 may be greater than50% (e.g., turned on).

In other words, FIG. 6 is a schematic of a single MEMS switch 600consisting of a movable optical coupler 614 and a fixed optical antenna616. The optical coupler 614 can be moved to be close enough to the buswaveguide so that a sufficient amount of light will be coupled out frombus waveguide 608 to the coupler waveguide 614. One example of such anoptical coupler can be tapered waveguide, and electrostatic actuatedcantilever can move the optical coupler up and down. The optical antenna616 is on the same layer with the optical coupler, but it is fixed. Thelight from the optical coupler can be emitted to free space via theoptical antenna, and vice versa, the light from free space can also becoupled back to the optical coupler via the optical antenna, thenfurther coupled back to the bus waveguide.

The MEMS switch includes a substrate 700 such as a silicon substratewith an insulating layer 702 such as silicon dioxide. On top of theinsulating layer 702 is a silicon layer 704. The first three layers(700, 702, 704) may be a Silicon on Insulator (SoI)substrate. The nextlayer may be an oxide 706, such as a low-temperature oxide (LTO), thatis used to form anchor points. The top layer may be a Silicon layer 708,such as a Poly-silicon layer that may be deposited via Plasma EnhancedChemical Vapor Deposition (PECVD) or Low Pressure Chemical VaporDeposition (LPCVD). In this embodiment, the structures such as buswaveguide 608 and MEMS actuation electrode 610 are in the silicon layer704 while the MEMS spring 612, the coupling cantilever 614, reactionelectrode, and the optical antenna 616 are in the poly-silicon layer708.

FIG. 7A is a cut view of the optical coupled cantilever of the MEMSswitch of FIG. 6 in an idle state. When in the idle or off state, thecantilever of the poly-silicon layer 708 may be a first distance fromthe bus waveguide of the silicon layer 704 as a voltage differencebetween the reaction electrode and the actuation electrode is less thanthe lower threshold. And the coupling efficiency between the buswaveguide 608 and the optical antenna 616 via the coupling waveguide 614is less than 1% (e.g., turned off).

FIG. 7B is a cut view of the optical coupled cantilever of the MEMSswitch of FIG. 6 in an actuated state. When in the on state, thecantilever of the poly-silicon layer 708 may be a second distance fromthe bus waveguide of the silicon layer 704 as a voltage differencebetween the reaction electrode and the actuation electrode is greaterthan the upper threshold. And the coupling efficiency between the buswaveguide 608 and the optical antenna 616 via the coupling waveguide 614is greater than 50% (e.g., turned on).

FIG. 7C is a cut view of the fixed optical antenna of the MEMS switch ofFIG. 6 in an idle state. When in the off state, the optical antenna ofthe poly-silicon layer 708 may substantially be the first distance fromthe bus waveguide of the silicon layer 704.

FIG. 7D is a cut view of the fixed optical antenna of the MEMS switch ofFIG. 6 in an actuated state. When in the on state, the optical antennaof the poly-silicon layer 708 is maintained substantially to be thefirst distance from the bus waveguide of the silicon layer 704.

FIGS. 7A-D illustrate the cross section of the optical coupler andoptical antenna in an ON and OFF state, respectively. The advantage ofthis concept is that it imposes less design restrictions on the MEMSswitch design than in current state of the art. The operation frequencyof the Lidar system requires very high switching/movement speeds. Thistranslates into a limitation of the translated mass which requires atrade-off with the antenna and coupler design. In this disclosure,however, the antenna remains static and thus can be designed with muchgreater freedom, e.g. it can have a larger in-plane extension verticalto the bus waveguide which translates into a favorable narrower emittedlight beam profile. For example, for the design in FIG. 6, the fan angleof the optical antenna can be larger, the area of antenna along buswaveguide and across waveguide can both be larger so that the outputbeam will be narrower. The narrower beam is helpful to reach a betterangular resolution in beam steering.

If the antenna is not fixed, the area of the antenna will be preferablyto be limited to 30×30 um² or less, with the antenna being fixed, thereis no such a limitation. In addition, the optical antenna can have morefreedom in terms of periods and aspect ratio, which can increase itsemission efficiency. For example, because there is no hard limitation ofthe surface area and mass of the fixed antenna, it can have a largerextension along the waveguide, meaning having more periods. The aspectratio is limited by the mass of the antenna. Without limitation on themass, the aspect ratio can be designed mainly based on the emissionefficiency rather than a trade-off between emission efficiency andantenna mass. And the optical coupler can be designed to have a smallerdimension and lighter weight without antenna being movable, therefore,fast switching operation and optimized output beam quality can beachieved in this MEMS switch design.

In another embodiment, more than one coupling cantilevers can be coupledto each antenna. They can be connected to opposite ends of the antennaproviding separate emit and receive channel. The emit cantilever wouldbe oriented towards the laser source whereas the receive cantileverwould be oriented towards the light detector using either the samewaveguide for light coupling or using separate waveguides. Separate emitand receive channels could be operated independently enabling additionalfunctionalities. For example, the light could be received from severalpixels surrounding the current emitting pixel thus increasing overalllight collection efficiency.

An array of MEMS switch can be organized in a rectangular pattern (FIG.8), round pattern or other patterns in an optical terminal. Combinedwith a lens, this terminal can work as an optical transmitter with theemitting beam steered to various directions (e.g., FIG. 8). FIG. 8 is aperspective view of an optical switch array system 800 transmitting anoptical signal. Here a substrate 802, can be a monolithic chip such as asilicon chip, Silicon on Insulator (SoI) chip, Silicon carbide chip.Silicon Nitride chip, or other monolithic MEMS chip, or the substratecan be a multi-chip module on a substrate. Each optical antennae 806 isconfigured to be aligned with a bus waveguide 810, for example in thisembodiment, there is a first bus waveguide 810 a, a second bus waveguide811 b, and a third bus waveguide 810 c. In this embodiment, each buswaveguide 810 coupled with a main bus waveguide via a type I switch 818.That is coupled with a light source 814 (e.g., laser, LED, etc.) suchthat light emitted from the light source 814 travels along a direction812 and it distributed via the type I switches 818 to the opticalantennae 806. Positioned near the chip is a lens 804 that is configuredto create a collimated beam of light 816 from optical antennae 806 viathe lens 804. In this embodiment, the beam of light 816 can becollimated by translating the lens 804 along an axis 808 perpendicularto substrate 802 and optical antennae 806, or by translating thesubstrate 802 and optical antennae 806 along an axis 809 perpendicularto lens 804.

Such terminal can also work as an optical receiver which can receivebeam coming back from various directions and couple the beam back to PIC(FIG. 9). FIG. 9 is a perspective view of an optical switch array system900 receiving an optical signal. Here a substrate 902, can be amonolithic chip such as a silicon chip, Silicon on Insulator (SoI) chip,Silicon carbide chip, Silicon Nitride chip, or other monolithic MEMSchip, or the substrate can be a multi-chip module on a substrate. Eachoptical antennae 906 is configured to be aligned with a bus waveguide910, for example in this embodiment, there is a first bus waveguide 910a, a second bus waveguide 910 b, and a third bus waveguide 910 c. Inthis embodiment, each bus waveguide 910 coupled with a main buswaveguide via a type I switch 918. That is coupled with a light detector924 (e.g., photo diode, photo transistor, CCD, etc.) such that light iscollected from the light detector 924 as the light travels along adirection 922 and is collected via the type I switches 918 that gatheredvia the optical antennae 906. Positioned near the chip is a lens 904that is configured to gather a beam of light 920 to optical antennae 906via the lens 904. In this embodiment, the beam of light 920 can befocused by translating the lens 904 along an axis 908 perpendicular tosubstrate 902 and optical antennae 906, or by translating the substrate902 and optical antennae 906 along an axis 909 perpendicular to lens904.

Such terminal can also work as a transceiver, which can both transmitand receive beam (FIG. 10). FIG. 10 is a perspective view of an opticalswitch array system 1000 receiving and transmitting an optical signal.Here a substrate 1002, can be a monolithic chip such as a silicon chip,Silicon on Insulator (SoI) chip, Silicon carbide chip, Silicon Nitridechip, or other monolithic MEMS chip, or the substrate can be amulti-chip module on a substrate. Each optical antennae 1006 isconfigured to be aligned with a bus waveguide 1010, for example in thisembodiment, there is a first bus waveguide 1010 a, a second buswaveguide 1010 b, and a third bus waveguide 1010 c. In this embodiment,each bus waveguide 1010 coupled with a main bus waveguide via a type Iswitch 1018. That is coupled with a light detector 1024 (e.g., photodiode, photo transistor, CCD, etc.) such that light is collected fromthe light detector 1024 as the light travels along a direction 1022 andis collected via the type I switches 1018 that gathered via the opticalantennae 1006. Positioned near the chip is a lens 1004 that isconfigured to gather a focus beam of light 1020 from optical antennae1006 via the lens 1004. In this embodiment, the beam of light 1020 canbe focused by translating the lens 1004 along an axis 1008 perpendicularto substrate 1002 and optical antennae 1006, or by translating thesubstrate 1002 and optical antennae 1006 along an axis 1009perpendicular to lens 1004. And, That is coupled with a light source1014 (e.g., laser, LED, etc.) such that light emitted from the lightsource 1014 travels along a direction 1012 and it distributed via thetype I switches 1018 to the optical antennae 1006. Positioned near thechip is a lens 1004 that is configured to create a collimated beam oflight 1016 from optical antennae 1006 via the lens 1004. In thisembodiment, the beam of light 1016 can be collimated by translating thelens 1004 along an axis 1008 perpendicular to substrate 1002 and opticalantennae 1006, or by translating the substrate 1002 and optical antennae1006 along an axis 1009 perpendicular to lens 1004. If such terminalworks as a transmitter only, an independent optical photodetector orphotodetector array, or a receiver like shown in FIG. 9 can be used asreceiver. Similarly, if such terminal uses as a receiver only, otheroptical emitter, emitter array, or transmitter similar to what shown inFIG. 8 can be used as an independent transmitter.

Although not limited to the embodiments presented, in the designembodiments mentioned above, the lens and/or the MEMS switch array chipcan be integrated with mechanical structure so that one or both of themcan move along z-direction, as shown in FIG. 8-10. The advantage ofincluding this freedom is to be able to adjust the distance between thelens and the MEMS switch array chip to maximize the transmittingefficiency and receiving efficiency from/into each pixel.

The proposed system can be used in chip-Lidar system, includingtime-of-flight (ToF) operation and frequency modulated continuous wave(FMCW) operation. In a chip-Lidar system, light is coupled onto onewaveguide of the PIC and then distribute into sub-waveguides. Theproposed MEMS switch can combine with other types of binary switches(FIG. 11) or splitter optical trees (FIG. 12) or switches and splitteroptical trees (FIG. 13) for light distribution. FIG. 11 is a perspectiveview of an optical switch array system 1100 including at least two typesof optical switches. Here a substrate 1102 is illustrated with acantilever coupling switch that is coupled with an optical antennae 1106that is configured to be aligned with a bus waveguide 1110, for examplein this embodiment, there is a first bus waveguide 1110 a, a second buswaveguide 1110 b, and a third bus waveguide 1110 c. In this embodiment,each bus waveguide 1110 coupled with a main bus waveguide via a type Iswitch 1118.

FIG. 11 shows a layout with two types of binary switches. Use thetransmitting terminal as an example, light is propagating in the mainwaveguide. At the intersection of the main waveguide and the rowwaveguide, there's the type I switch to selectively guide the light intothe selected row (the row of waveguide 1110 b is selected in thisexample). And then light propagates in the selected row waveguide untilit reaches the MEMS switch (switch type II) that is in ON state andemits out. The type I switch can be either MEMS switch or other switchessuch as thermo-optic switch, electro-optic switch, etc. FIG. 12 shows alayout with splitter trees and binary MEMS switches. FIG. 12 is aperspective view of an optical switch array system 1200 including asplitter tree and an optical switch. Here a substrate 1202 isillustrated with a cantilever coupling switch that is coupled with anoptical antennae 1206 that is configured to be aligned with a buswaveguide 1210, for example in this embodiment, there is a first buswaveguide 1210 a, a second bus waveguide 1210 b, a third bus waveguide1210 c, and a fourth bus waveguide 1210 d. In this embodiment, each buswaveguide 1210 is coupled with a main bus waveguide via a splitter tree1218. Also, FIG. 12 illustrates a cantilever coupling and opticalantenna 1206 a in an off state, and a cantilever coupling and opticalantenna 1206 b in an on state such that light 1216 is radiated from theoptical antenna 1206 b via the coupling cantilever that is coupled withthe bus guide 1210 c when the coupling cantilever and optical antenna1206 b is turned on. The difference between these two layouts is that inthe splitter tree layout, the optical power from the laser isdistributed evenly into the waveguides, while in the combined binaryswitch layout, the light from the laser is selectively guided to adesired waveguide.

These two layout can be combined in a third layout, as shown in FIG. 13.FIG. 13 is a perspective view of an optical switch array system 1300including a splitter tree and at least two types of optical switches.Here a substrate 1302 is illustrated with a cantilever coupling switchthat is coupled with an optical antennae 1306 that is configured to bealigned with a bus waveguide 1310, for example in this embodiment, thereis a first bus waveguide 1310 a, a second bus waveguide 1310 b, and athird bus waveguide 1310 c. In this embodiment, each bus waveguide 1310is coupled with a main bus waveguide via a splitter tree 1318 and a typeI switch 1328. Also, FIG. 13 illustrates a cantilever coupling andoptical antenna 1306 a in an off state, and a cantilever coupling andoptical antenna 1306 b, 1306 c, 1306 d and 1306 e in an on state suchthat light is radiated from the optical antenna 1306 b, 1306 c, 1306 d,and 1306 e via the coupling cantilever that is coupled with the busguide 1310 b, 1310 e, 1310 h and 1310 j when the coupling cantilever andoptical antenna 1306 b, 1306 c, 1306 d, and 1306 e is turned on. In thislayout, light from the laser is distributed into several sections ofwaveguide subarrays, then in each waveguide subarray, binary switchesare used to selectively guide the light to desired waveguides. Thislayout enables the MEMS switches in various subarrays to be controlledindependently and simultaneously. All these layout can work in the MEMSswitch array based transmitting, receiving and transceiving terminals.

One advantage of the MEMS switch array is the relatively simple controlelectronics. FIGS. 14 and 15 shows two example of the electroniccontrols to electrostatically actuate the MEMS switch array.

FIG. 14 is a diagram of a switch array system 1400 configured toindependently address rows and columns. This system 1400 addressescolumns via a column contact controller 1404 and addresses rows via arow contact controller 1406. In this illustration, columns contactcontroller 1404 c is enabled thus turning on selected or all switchesassociated with that columns, and row contact controller 1406.3 isenabled thus turning on the wave guide associated with that switch. Theresult includes turning on optical switch 1408 enabling light 1410 to beemitted from a single optical switch of the array. FIG. 15 is a diagramof a switch array system 1500 configured to address sub arrayssimultaneously. This system 1500 addresses columns via a contact contactcontroller 1504 and addresses rows via a row contact controller 1506. Inthis illustration, column contact controller 1504 b is enabled thusturning on selected or all switches associated with that column, and rowcontact controller 1506.11, 1506.8, 1506.5, and 1506.3 are enabled thusturning on the wave guide associated with those switches. The resultincludes optical switch 1512 a, 1512 b, 1512 c, and 1512 d turning onand enabling light 1514 a, 1514 b, 1514 c and 1514 d to be emitted froma single optical switch of the array.

In other words, one way to actuate the MEMS switches in the array is ofcourse to have each switch individually addressed, therefore, if thereare M×N switches in the array in which M is the number of rows and N isthe number of columns, there will need M×N controls. One exampleapproach to simplify the control is to address rows and columns (asshown in FIG. 14), so that M×N switches only need M+N controls. In FIG.14, the switchable pixel that is illuminating is enabled by applying theright amount of voltage to row-1406 and column-1404. Another exampleapproach is to split the MEMS switch array into subarrays, and addressthe switch in multiple subarrays simultaneously, as shown in FIG. 15. InFIG. 15, four switchable pixels are illuminating simultaneously, andthey are enabled by applying suitable voltages on column-1504, row-3,row-5, row-8 and row-11 to actuate the corresponding MEMS switches. Andof course, the subarrays can be addressed individually too. All theseelectronic control approaches can work in the MEMS switch array basedtransmitting, receiving and transceiving terminals. The advantages ofthe control method shown in FIG. 14 and FIG. 15 is the simplicity. Theamount of controls is significantly decreased compared to the individualcontrolled switches.

FIG. 16 is a perspective view of a bus waveguide and a correspondingcoupler waveguide on an optical switch 1600. A substrate 1602 supports abus waveguide 1604 aligned with the bus waveguide 1604 is a cantilevercoupler 1610 that is separated from the bus waveguide 1604 by a verticalgap 1606. The cantilever coupler 1610 may be tapered such that it has anarrow tip 1608 and a wider base 1612. For example, the tip 1608 may bea point, a rounded tip, or have a blunt end in which a ratio of the tip1608 to the base 1612 include 1:3, 1:4, 1.5, etc. For example, a tipwidth 1608 may be 0.08, 0.1, 0.15, 0.2 um while the base 1612 may be0.2, 0.3, 0.4, 0.5, etc. The length of the cantilever coupler 1614 issuch that the cantilever coupler can be deflected to reduce the gap 1606such that a coupling efficiency between the wave guide 1604 and thecantilever coupler 1610 is above a threshold such as 50%, 60%, orgreater. It should be noted that typically two actuation electrodes areon the substrate 1602 parallel with the bus waveguide 1604 with oneelectrode on either side of the bus waveguide 1604, the length of theelectrodes is approximately equal to the length of the cantilevercoupler 1610. Likewise, typically there are two reaction electrodes areon the cantilever coupler 1610 substantially parallel with the buswaveguide 1604 with one electrode on either side of the cantilevercoupler waveguide outlined by the narrow tip 1608 and wide base 1612.The length of the reaction electrodes is approximately equal to thelength of the cantilever coupler 1610.

FIG. 17 is a graphical representation of coupling field profile 1700with respect to distance. This illustrates a field profile when acoupling cantilever is turned on and energy is transferred from the buswave guide to the cantilever waveguide. This illustration is associatedwith the cantilever coupler of FIG. 16 with a length of 7.5 umillustrating transfer of energy over the length of the cantilevercoupler. Similarly, FIG. 18 is a series of 2-dimension graphicalrepresentations of coupling field profiles 1800 with respect topropagation distance. This illustrates a field profile when a couplingcantilever is turned on and energy is transferred from a bus waveguide.This illustration is associated with the cantilever coupler of FIG. 16with a length of 7.5 um illustrating transfer of energy over the lengthof the cantilever coupler.

FIG. 19 is a graphical representation 1900 of coupling efficiency 1902with respect to coupling taper length 1904. This illustrates a couplingefficiency 1906 when a coupling cantilever with various taper lengths isturned on and energy is transferred from a bus waveguide. Thisillustration is associated with the cantilever coupler of FIG. 16 withvarious taper lengths illustrating transfer of energy over the length ofthe cantilever coupler. FIG. 20 is a graphical representation 2000 oftransmission loss 2002 with respect to wavelength 2004. This illustratesa transmission loss 2002 when a coupling cantilever is turned on andenergy is transferred from a waveguide. This illustration is associatedwith the cantilever coupler of FIG. 16 with a length of 7.5 umillustrating transmission loss 2002 over the length of the cantilevercoupler. As stated in this disclosure, the cantilever coupler is notlimited to a Silicon, however in this example, the cantilever coupler isa Silicon cantilever coupler.

FIG. 21 is a graphical representation 2100 of energy loss 2102 withrespect to gap size 2104. In this illustration, the energy to bus 2106has a minimum at approximately 180 nm at which point the energy to MEMS2108 begins to deflect and drop off. Based on this, during the “ON”state, the gap is maintained substantially at 180 nm to ensure maximumcoupling efficiency to the MEMS waveguide. In an “OFF” state, the gapreturns to a distance above a distance for example 650 nm such that aresulting energy to MEMS is less than −30 dB. FIG. 22 is a graphicalrepresentation 2200 of a radiation pattern 2206 with respect to an angleβ 2202 (as illustrated in FIG. 5B angle 562) and an angle θ 2204 (asillustrated in FIG. 5B angle 560). In FIG. 22, the energy intensity isnormalized to a 1 based on the grey scale and the contour lines areshown as the radiation patterns 2206.

FIG. 23 is a side view illustration of an optical system 2300 includinga waveguide grating 2302 in a waveguide 2304. The waveguide may be amaterial such as silicon, polysilicon, silicon nitride, silicon carbide,silicon dioxide, or other material that can be configured to conduitenergy (e.g., a waveguide). The grating 2302 includes gaps 2310 that mayvary from 100 nm to 500 nm or more at a pitch 2312 that can be a factorof 1.5, 2.0, or 2.5 times the gap 2310 distance. The gap distance mayvary across a plane perpendicular with the underlying wave guide.Performance of the waveguide can be evaluated along a plane 2314substantially parallel with substrate and a distance 2316 above thesubstrate. The energy diffracts into free space substantially at anangle θ 2318 that is incident to the plane 2314. FIG. 24 is aperspective view of a cantilever spring 2400 illustrating displacementthat results from biasing between a reaction electrode and actuationelectrode at a voltage. For example a voltage difference of 40V betweenthe reaction electrode and actuation electrode illustrating adisplacement of substantially 620 nm. FIG. 25 is a graphicalrepresentation 2500 of displacement along a Z-axis 2502 with respect toswitching speed 2504. This graphical representation shows thedisplacement along the Z-axis of FIG. 24 at different locations of thecantilever waveguide. In this example, three profiles are displayed, adisplacement near the tip of the cantilever waveguide 2506, adisplacement at the middle towards the end of the cantilever waveguide2508 and a displacement near the end where it is connected to theoptical antenna 2510.

FIG. 26 is a top view of a switch array layout 2600 with multipleoptical switches on a substrate 2602 and a detailed illustration of asingle element 2604. The optical switch includes a wave guide 2606coupled with the substrate 2602 also coupled with the substrate is ananchor point 2608. A MEMS spring 2610 is shown coupled with one anchorpoint 2608, while an optical grating 2612 is coupled with another anchorpoint 2608. The MEMS spring 2610 has a first end coupled with the anchorpoint 2608 and a second end coupled with a cantilever coupler 2614 thatis suspended above the bus waveguide 2606. Mounted to the substrate 2602on either side of the bus waveguide 2606 is an actuation electrode, andmounted on either side of the cantilever coupler 2614 is a reactionelectrode that is configured to corporate with the actuation electrode.In this illustration, the optical grating/optical antenna 2612 is on thesame layer as the cantilever coupler 2614. In an optical switch arraysystem for beam steering applications, one embodiment includes a systemin which each optical switch consists of a movable MEMS optical coupleron a suspending layer and an optical antenna on the substrate layer. TheMEMS optical coupler enabled switch array can be used to couple lightfrom waveguide on photonic integrated circuit (PIC) chip to free space(or vice versa) in various applications including Lidar.

FIG. 27A is a perspective view of a switch array 2700 with movableoptical coupler 2714 on a suspension layer 2716 and a fixed opticalantenna 2712 on a substrate layer 2702. FIG. 27B is a top view of theswitch array 2700 with movable optical coupler on a suspension layer anda fixed optical antenna on a substrate layer. The optical switchincludes a waveguide 2706 coupled with the substrate 2702 also coupledwith the substrate is an anchor point 2708. A MEMS spring 2710 is showncoupled with one anchor point 2708. The MEMS spring 2710 has a first endcoupled with the anchor point 2708 and a second end coupled with acantilever coupler 2714 via the suspension layer 2716 that is suspendedabove the bus waveguide 2706. Mounted to the substrate 2702 on eitherside of the bus waveguide 2706 is an actuation electrode 2718, andmounted on either side of the cantilever coupler 2714 is a reactionelectrode 2716 that is configured to corporate with the actuationelectrode 2718. In this illustration, the optical grating/opticalantenna 2712 is on the same layer as the bus waveguide 2706.

The MEMS switch array may be enabled by movable MEMS optical coupler2714 on a suspending layer 2716 and fixed optical antenna 2712 onsubstrate layer 2702. FIGS. 27A and 27B provide a perspective view andtop view of such a MEMS switch. Each MEMS switch consists of a movableMEMS optical coupler 2714 on the suspending layer 2716 (we call “MEMSlayer”), and an optical antenna 2712 on the substrate layer 2702. Heregrating antenna 2712 is used as an example to illustrate the concept,other optical antenna designs also work for this concept. When in an OFFstate, the MEMS layer, reaction electrode 2716, and cantilever coupler2714 are far away from the bus waveguide 2706 and actuation electrode2718 such that light can propagate in the bus waveguide 2706unperturbed. When in an ON state, the reaction electrode 2716 isactuated and moves the MEMS optical coupler 2714 close to the buswaveguide 2706, such that light is coupled to the coupler waveguide 2714on the MEMS layer with the reaction electrode 2716 a second cantilevercoupler drops to a detached bus waveguide that is connected to theoptical antenna 2712, which transmits signal to free space. This lightpath is reversed when receiving a signal.

FIG. 28A is a cross sectional view of the movable optical coupler ofFIG. 27 while in the OFF position. When in an OFF state, the MEMS layer(that includes the reaction electrode) 2716 is over the top of the buswaveguide 2706 at a first distance. The distance is due to a voltagedifference between the actuation electrode 2718 and the reactionelectrode 2716 being below a voltage threshold such that the cantilevercoupler 2714 is far away from the bus waveguide 2706. The first distanceis such that light propagates in the bus waveguide 2706 substantiallyunperturbed.

FIG. 28B is a cross sectional view of the movable optical coupler ofFIG. 27 while in the ON position. When in an ON state, the MEMS layer(that includes the reaction electrode) 2716 is over the top of buswaveguide 2706 at a second distance. The second distance is due to avoltage difference between the actuation electrode 2718 and the reactionelectrode 2716 being above the voltage threshold such that thecantilever coupler 2714 is pulled towards the bus waveguide 2706. At thesecond distance, light is coupled to the coupler waveguide 2714 on theMEMS layer with the reaction electrode 2716 and a second cantilevercoupler that drops to a detached bus waveguide that is connected to theoptical antenna 2712, which transmits signal to free space. This lightpath is reversed when receiving a signal.

FIGS. 28A and 28B illustrates a cross-section of the actuation of theoptical coupler. The advantage of this concept is that the opticalantenna is on the substrate layer, which does not add weight to thesuspending structure and has fewer fabrication challenges compared toother structures. The operation frequency of a Lidar system requiresvery high switching/movement speeds. This translates into a limitationof the translated mass. In the present disclosure, however, the opticalantenna remains on the substrate layer so that its dimension does notaffect the operation speed. As a result, the antenna can have a largerfootprint to form a favorable Gaussian beam profile, and the emissionefficiency can be optimized by flexible grating periods and/or dutycycle. The coupler waveguide on the suspending layer is small and lightweight, which further promises fast switching speed. The optical couplercan be actuated electrostatically, piezoelectrically or by othermechanisms. It can be a dual cantilever with the middle part anchoredsuch that both ends can be operated together or both ends can beoperated independently. Also it can be a beam in which the entirecoupler waveguide moves during operation (as shown in FIG. 27B).

The concepts described in here can be implemented in alternativeembodiments. Another embodiment is shown in FIGS. 29 and 30. FIG. 29 isa top view of a switch array layout 2900 with a movable optical coupler2914 on a suspension layer and a fixed optical antenna 2912 on asubstrate layer 2902 with a detailed illustration of a single element.The optical switch includes a wave guide 2906 coupled with the substrate2902 also coupled with the substrate is an anchor point 2908. A MEMSspring 2910 is shown coupled with one anchor point 2908. The MEMS spring2910 has a first end coupled with the anchor point 2908 and a second endcoupled with a cantilever coupler 2914 via the suspension layer 2916that is suspended above the bus waveguide 2906. Mounted to the substrate2902 on either side of the bus waveguide 2906 is an actuation electrode2918, and mounted on either side of the cantilever coupler 2914 is areaction electrode that is configured to corporate with the actuationelectrode 2918. In this illustration, the optical grating/opticalantenna 2912 is on the same layer as the bus waveguide 2906.

FIG. 30 is a top view of a switch array layout 3000 with a movableoptical coupler on a suspension layer and a fixed optical antenna on asubstrate layer with a detailed illustration of a single element. Theoptical switch includes a waveguide 3006 coupled with the substrate 3002also coupled with the substrate is an anchor point 3008. A MEMS spring3010 is shown coupled with one anchor point 3008. The MEMS spring 3010has a first end coupled with the anchor point 3008 and a second endcoupled with a cantilever coupler 3014 via the suspension layer 3016that is suspended above the bus waveguide 3006. Mounted to the substrate3002 on either side of the bus waveguide 3006 is an actuation electrode3018, and mounted on either side of the cantilever coupler 3014 is areaction electrode that is configured to corporate with the actuationelectrode 3018. In this illustration, the optical grating/opticalantenna 3012 is on the same layer as the bus waveguide 3006.

The layout in FIG. 29 consists of an array of straight waveguides withan array of optical antennas 2912 locating at an offset distance fromthe waveguides 2906. In this design, the coupler waveguide 2914 makes aturn to pick up light from bus waveguide 2906 and drop it to the antenna2912. Alternatively, the layout in FIG. 30 consists of an array ofcurved bus waveguides 3006 with an array of optical antennas 3012aligned to the straight parts of the bus waveguide 3006. In this design,the coupler waveguide is straight.

FIG. 31 is a top view of an element of a switch array layout 3100 withan optical coupler 3126 on a suspension layer 3124 and a fixed opticalantenna 3104 on a substrate layer. The optical antenna 3104 covers anangle 3106, such as 45 degrees, 60 degrees, or 90 degrees, and has abase or taper 3108 after which the grating begin. The optical coupler3126 may be a single element or consist of multiple segments. Here theoptical coupler 3126 has three segments, the first segment 3112 is thesegment that is drawn down to couple with the optical antenna 3104 whenactivated. The second segment 3114 connects the first segment 3112 withthe third segment 3116. The third segment 3116 is the segment that movesdown to couple with the bus waveguide 3102. The second segment 3114 maybe stationary and directly coupled with an anchor point such that thedistance from the second segment 3114 to the substrate does not move, orin another embodiment, the second segment 3114 is floating and moveswith the movement of the first 3112 and third segments 3116. The buswaveguide 3102 may have a width 3118 at a point at which the tip of theoptical coupler 3126 will couple when activated, and that width maynarrow to a width 3120 prior to a turn of radius 3122 such that the turnis configured to be substantially adiabatic. The transmission throughthe optical coupler 3126 may have a first loss 3128 through the thirdsegment 3116, a second loss 3130 through the second segment 3114, and athird loss 3132 through the first segment 3112. These losses may be afraction of a dB, for example, the first 3128 and third 3132 may be 0.1dB while the loss in the second segment 3130 may be less than 0.02 dB.FIG. 32 is a cross sectional view of the element 3200 of FIG. 31. Herethe optical coupler 3126 is coupled with the suspension layer 3124 andaligned over the bus waveguide 3102. The optical bus waveguide 3102 hasa height 3210 and the suspension layer 3124 is a distance 3212 above thebus waveguide 3102, that distance changes with state, for example, whenon, the distance 3212 may be less than 0.2 microns and when off thedistance 3212 may be greater than 0.6 microns. The suspension layer 3124may have a thickness 3214 such that it can provide support yet stillallow for optical coupling between the bus waveguide 3102 and theoptical coupler 3126. The optical coupler 3126 may have a thickness of3216.

FIG. 31 and FIG. 32 shows an example of a single MEMS optical couplerand a fixed grating antenna in the FIG. 30 layout. The dimensionslabeled in FIG. 31 is an example, FIGS. 17 and 18 shows its couplingperformance with the MEMS optical coupler being 180 nm away from the buswaveguide, and FIG. 33 shows the electrical field distribution on thegrating. FIG. 33 is a graphical representation of a field profile 3300of a grating antenna with respect to X coordinates 3304 and Ycoordinates 3302. FIG. 34 is a perspective view of an illustratingdisplacement of an optical coupler 3400 such as the optical coupler ofFIG. 31. FIG. 34 is a simulation of the displacement of a MEMS opticalcoupler. In general the optical coupling length ranges from severalmicro-meters to hundreds of micro-meters depending on different designs,and the distance between the coupler waveguide and the buswaveguide/antenna waveguide ranges from several nanometers to severalmicrons at ON state.

Some optical antennas have non-zero emission angle θ, as shown in FIG.35 and FIG. 36, which may raise an issue in the amplitude arrayterminal. FIG. 35 is a perspective view of a grating antenna 3500 of aMEMS structure 3502 illustrating emission angles β 3504 and θ 3506. FIG.36 is a graphical representation of intensity 3600 with respect toemission angles β 3602 and θ 3604. In this figures, 10 periods are shownin which the intensity is illustrated via a gray scale.

One solution to this problem is to sacrifice the optical antennaradiation efficiency and far-field beam quality to get a zero emissionangle. The second solution is to add additional structure to force lightemit vertically, including but not limited to bottom reflector,additional top dielectric layer, extra-fine etching groove. The thirdsolution is to design the lens accordingly to compensate for thenon-zero emission angles. However, it is not flexible enough to addressdifferent emission angles due to fabrication fluctuations. Here wepropose to use a mirror or prism between the antenna array and the lensto compensate for the non-zero emission angle, as shown in FIG. 39, 40,41. FIG. 39 is a side view 3900 illustrating a mirror to compensate fora non-zero antenna emission angle. Here a telecentric lens 3902 is usedto collimate the light from antenna array or photonic integrated circuitto free space through a mirror (transmitting), or reflect off a mirror3904 to an antenna array or photonic integrated circuit (PIC) 3910(receiving). Here a virtual image 3906 of the PIC 3910 is shown on avirtual plane 3908. FIG. 40 is a side view illustrating an optical prismsystem 4000 to compensate for a non-zero antenna emission angle. Here atelecentric lens 4002 is used to collimate the light from an antennaarray to free space through a prism (transmitting) or focus lightthrough a prism to an antenna array 4004 (PIC) (receiving). FIG. 41 is aside view 4100 illustrating a micro-prism array to compensate fornon-zero antenna emission angle. Here a telecentric lens 4102 is used tocollimate the light from an antenna array to free space through microprisms (transmitting) or focus light through micro prisms to an antennaarray 4104 (PIC)(receiving).

The mirror or prism can bend the light so that the reflected orrefracted rays incident onto the lens system with zero incidence angle.Because the mirror or prism can rotate, they can be adjusted during thecalibration stage to compensate for the fabrication errors. Meanwhile, atelecentric lens can be used to match the tilted emission array. Theadvantage of this approach is that it does not require complicated lensdesign.

The proposed system can be used in chip-Lidar system, includingtime-of-flight (ToF) operation and frequency modulated continuous wave(FMCW) operation. In a chip-Lidar system, light is coupled onto onewaveguide of the PIC and then distributed into sub-waveguides. FIG. 42Ais a top view of an antenna array 4200 with splitter trees 4202 andoptical switches 4204. FIG. 42B is a top view of an antenna array 4230with multiple switch types, in this example, there are type I switches4206 and optical switches 4204. FIG. 42C is a top view of an antennaarray 4360 with splitter trees 4202 and multiple switch types such astype I switches 4206 and optical switches 4204. The proposed MEMS switchcan be combined with splitter trees (FIG. 42A) or other types of binaryswitches (FIG. 42B) or switches and splitter trees (FIG. 42C) for lightdistribution. FIG. 42B shows a layout with two types of binary switches.Referring to the transmitting terminal as an example, light ispropagating in the main waveguide. At the intersection of the mainwaveguide and the row waveguide, type I switch can selectively guide thelight into the selected row (the second row from the top is selected inthe drawing). Then light propagates in the selected row waveguide untilit reaches the ON state MEMS switch (switch type II) and emits out. Thetype I switch can be either MEMS switch or other switches such asthermo-optic switch, electro-optic switch, etc. FIG. 42A shows a layoutwith splitter trees. The difference between these two layouts is that inthe splitter tree layout, the optical power from the laser isdistributed evenly into the waveguides, while in the combined binaryswitch layout, the light from the laser is selectively guided to onewaveguide at a time. These two layouts can be combined in a thirdlayout, as shown in FIG. 42C. In this layout, light from the laser isdistributed into several sections of waveguide subarrays, then in eachwaveguide subarray, binary switches are used to selectively guide thelight to desired waveguides. This layout enables the MEMS switches invarious subarrays to be controlled independently and simultaneously. Allthese layouts can work in the MEMS switch array basedtransmitting/receiving terminals. In the layout of FIG. 42B and FIG.42C, the active row is selected by the type I switch, while the activecolumn is selected by the type II switches. Therefore, the controlcomplexity for a M×N array scales linearly with the array size (O(M+N))rather than quadratically (O(M×N)).

This section will disclose MEMS switch and arrays moving in-the-planefor optical coupling. The proposed MEMS switches can be used to couplelight from waveguide on photonic integrated circuit (PIC) chip to freespace in various applications.

FIG. 43A is a perspective view of a switch array with a moveable gratingthat travels longitudinally with multiple stop positions. In thisembodiment, the grating 4308 travels longitudinally such that there aremultiple stopping positions, this illustration shows 3 stoppingpositions, 4308 a, 4308 b, and 4308 c. In this embodiment, the neutralposition may be 4308 a such that based on voltage applied to theinterdigitated electrodes will move the grating to the other positions4308 b, and 4308 c. Also, the grating may be configured such that theneutral position is in the middle 4308 b, such that a positive voltageacross the interdigitated electrodes moves the grating to one position(e.g., 4308 a) and a negative voltage across the interdigitatedelectrode moves the grating to the other position (e.g., 4308 c). Inthis illustration, the light travels down the waveguide 4304 and tothree bus waveguides 4306 a, 4306 b, and 4306 c. As describedpreviously, the light may travel down via a beam splitter, or an opticalswitch, and the light may also travel in the opposite direction of 4304.FIG. 43B is a perspective detailed view of a moveable grating 4314 thattravels longitudinally 4312 with multiple stop positions to the buswaveguide 4316 from FIG. 43A. The bus waveguide 4316 is supported by thesubstrate. The substrate supports an anchor 4318 which is coupled withthe interdigitated electrodes 4320.

FIG. 43C is a perspective view of a switch array with a moveable grating4328 that travels longitudinally 4322 to the bus waveguide 4326. Thisillustration shows 2 stopping positions, 4328 a and 4328 b. In thisembodiment, the neutral position may be 4328 a such that based onvoltage applied to the interdigitated electrodes will move the gratingto the other position 4328 b. In this illustration, the light travelsdown the waveguide 4324 and to three bus waveguides 4326 a, 4326 b, and4326 c. As described previously, the light may travel down via a beamsplitter, or an optical switch, and the light may also travel in theopposite direction of 4324. FIG. 43D is a perspective detailed view oftwo moveable gratings 4342 that travel longitudinally to the buswaveguide 4316 from FIG. 43C. The bus waveguide 4316 is supported by thesubstrate. The substrate supports an anchor 4338 which is coupled withthe interdigitated electrodes 4334. FIG. 43E is a top view of a movablegrating 4342 that travels longitudinally 4332 to the bus waveguide 4336via interdigitated electrodes 4334. The bus waveguide 4336 is supportedby the substrate. The substrate supports an anchor 4338 which is coupledwith the interdigitated electrodes 4334. A spring 4340 is coupled withthe grating 4342 on one side and an anchor 4338 on the other.

FIG. 44A is a perspective view of a switch array with a moveable grating4408 that travels transversely 4402 to the bus waveguide 4406 withmultiple stop positions. In this embodiment, the grating 4408 travelstransversely such that there are multiple stopping positions, thisillustration shows 3 stopping positions, 4408 a, 4408 b, and 4408 c. Inthis embodiment, the neutral position may be 4408 a such that based onvoltage applied to the interdigitated electrodes will move the gratingto the other positions 4408 b, and 4408 c. Also, the grating may beconfigured such that the neutral position is in the middle 4408 b, suchthat a positive voltage across the interdigitated electrodes moves thegrating to one position (e.g., 4408 a) and a negative voltage across theinterdigitated electrode moves the grating to the other position (e.g.,4408 c). In this illustration, the light travels down the waveguide 4404and to three bus waveguides 4406 a, 4406 b, and 4406 c. As describedpreviously, the light may travel down via a beam splitter, or an opticalswitch, and the light may also travel in the opposite direction of 4404.FIG. 44B is a perspective detailed view of a moveable grating 4408 thattravels transversely 4402 to the bus waveguide 4406 with multiple stoppositions of the switch array from FIG. 44A. The bus waveguide 4406 issupported by the substrate. The substrate supports an anchor 4418 whichis coupled with the interdigitated electrodes 4420. FIG. 44C is a topview of a movable grating 4442 that travels transversely to the buswaveguide 4436 via interdigitated electrodes 4434. In this illustrationa spring 4440 is coupled with an anchor 4438 that is coupled with thesubstrate. The other end of the spring 4440 is coupled with the grating4442 such that force applied by the interdigitated electrodes 4434 willmove the grating 4442 to be over a bus waveguide 4436 as describedabove.

FIG. 45 is a perspective view of a switch array with a moveable gratingthat travels transversely 4502 with stop positions in-plane andoff-plane with waveguides 4506. In this embodiment, light travels downthe bus waveguide in a direction 4504 and is distributed to three buswaveguides 4506 a, 4506 b, and 4506 c. In this embodiment, grating thatare off-plane, are shown as 4510 and are not aligned with any buswaveguide 4506. Grating that are in-plane, are shown as 4508 and arealigned with a bus waveguide 4506 such that there is optical couplingbetween the grating 4508 and the bus waveguide 4506 b.

FIGS. 43, 44 and 45 show three examples of in-plane movable MEMSswitches in the amplitude array Lidar application. In all of these threefigures, grating antenna are used as an example to illustrate the switchconcepts, other antenna designs would also work for these switchconcepts. In all these three designs, the MEMS switch layer issuspending above the bus waveguide layer. The gap distance between theMEMS switch layer and bus waveguide layer is several nanometers tohundreds of nanometers so that the coupling efficiency between the MEMSswitch and bus waveguide is sufficient for more than 50% of the light tobe coupled from bus waveguide to MEMS switch layer. In FIG. 43, the MEMSswitches can move along the waveguide, and the pixels are virtual pixelswhich are defined by the stop position of the MEMS switch. Whenever theMEMS switch stops, the light coupled out from that position, and thatvirtual pixel is turned on. Depending on the dimension of the waveguideand the movement range of the MEMS switch, there could be one (FIGS. 43Aand 43B) or more than one (FIGS. 43C and 43D) MEMS switch covering onewaveguide length. In FIG. 44, the MEMS switches can move in-plane alongx-direction across multiple waveguides. Similar to the design in FIG.43, the pixels are also virtual pixels defined by the stop position ofthe MEMS switches. Depending on the dimension of the waveguide array andthe movement range of the MEMS switch, one MEMS switch can cover all thewaveguides in the array or partial waveguides in the array. Oneadvantage of the MEMS switch shown in FIG. 43 and FIG. 44 is that theswitches move in-plane, which is easier to be implemented than theout-of-plane movable switches. Also, the virtual switch stops allowswitches to stop at any position along the movement path flexibly.

FIG. 45 shows another in-plane MEMS switch design. Different than thedesign in FIG. 44, the pixels here are real pixels defined by therelative overlap of MEMS switches and bus waveguides. In OFF state, theswitches are located off the waveguides, and in ON state, the switchmoves to have overlap with the waveguide. Its advantage is that themovement distance for each switch is small so that the switches areeasier to implement.

The proposed in-plane MEMS switches can also be organized in an arrayand combine with lens to do beam steering in optical transmitter,receiver, or transceiver terminals. All the switch combination andsplitter tree combination concepts and row/column wiring concepts alsowork with the proposed in-plane MEMS switches.

The concepts of a vertically movable MEMS switch with cantilever couplerand fixed optical antenna as presented in this disclosure requirestopping the cantilever coupler. For the vertically movable MEMSswitches (e.g., FIGS. 4A-4C, FIG. 6), stopping the MEMS switch oroptical cantilever at a certain distance away above the bus waveguideneeds to be controlled. A mechanical stoppers (a bump) may be used tomechanically stop the MEMS switches. However, as the suspending layerwill contact the mechanical stoppers in every operation, the mechanicalstoppers may wear out and may thereby degrade light coupling performanceof the system. Here a system and method of electrostatic levitation isused as a MEMS switch stopper in the MEMS switch light couplingapplication.

FIG. 46 is a perspective view of a switch 4600 with electrostaticlevitation to control a coupling distance between a bus waveguide andthe gratings. The electrostatic levitated switch 4600 has a substrate4602 that supports bottom side or repulsion electrodes 4604, a buswaveguide 4606, bottom center or activation electrodes 4608, and anchors4614. Supported above the bus waveguide 4606 is an optical grating 4610suspended by a spring 4612 that is coupled with the anchor 4614.Positioned on the grating 4610 is a top or reaction electrode 4616. Themethods of controlling the stop position of vertically movable MEMSswitches with non-mechanical stoppers are described. One method ofutilizing electrostatic levitation is shown in FIG. 46 (switchable MEMSgrating is used as an example to illustrate the concept). In such adesign, the bottom center electrodes and top electrodes are used toelectro-statically actuate the MEMS structure to the pull-in or beyondthe pull-in state, then the bottom center electrodes and top electrodesare kept in the same voltage level (for example, both are ground), and alarge positive voltage is applied to the bottom side electrodes.Therefore, the large electric field generated by the bottom sideelectrode voltage push the MEMS structure up, and eventually hold thestructure a certain distance above the bus waveguide. The advantage ofthe electrostatic levitation stopper is that the suspending layer doesnot physically touch the bottom bus waveguide layer, so that there's nostiction problem or physical wearing-out concerns during the MEMSoperation. However, this method request relatively high voltage to holdthe suspending layer at a certain position.

Another method is to use comb drive, one example is shown in FIGS. 47Aand 47B. FIG. 47A is a perspective view of a switch 4700 with a combdrive to control a coupling distance between a bus waveguide 4706 andthe gratings 4710. The electrostatic comb levitated switch 4700 has asubstrate 4702 that supports bottom side or activation comb electrodes4704, a bus waveguide 4706, and anchors 4714. Supported above the buswaveguide 4706 is an optical grating 4710 suspended by a spring 4712that is coupled with the anchor 4714. Coupled with the optical grating4710 is a top or reaction comb electrode 4708. FIG. 47B is across-sectional view along a cut of FIG. 47A illustrating the comb drivein which the bottom side or activation comb electrodes 4704 areinterdigitated with the top or reaction comb electrode 4708 adjacent tothe bus waveguide 4706. In this illustration, the fins of the comb driveare perpendicular with the bus waveguide 4706, but the fins may also beconfigured to be parallel with the bus waveguide 4706.

Finger electrodes are formed on the movable suspending layer (topelectrodes) and fixed substrate layer (bottom electrodes). The electricfield direction between top and bottom electrodes can be controlled bythe polarity of voltages added to the electrodes. When the voltage addedto top electrodes is higher than the bottom electrodes, electric fieldis going downward and can pull the suspending layer to move towards thebus waveguide. Once it reaches a certain position, changing the topelectrodes voltage to be smaller than the bottom electrodes, theelectric field is going upward and can help overcome the gravity andhold the suspending layer at a certain position. The advantage of combdrive is that it does not request as much voltage as electrostaticlevitation, and it's also a non-mechanical stopper.

In this disclosure, various designs of MEMS switches and switch arrayshave been disclosed. Those various designs being used in the opticaltransmitting, receiving and transceiving terminals. Now methods ofintegrating the MEMS switches and switch arrays into a chip-Lidarsystem, and packaging such system is described.

MEMS switch array based chip-Lidar system integrate MEMS structures ontoa silicon photonics platform. This combination of MEMS structure andsilicon photonics platform raises new challenges that are not present inMEMS-only systems and silicon-photonics-only systems. Therefore, systemintegration and packaging needs to be well designed and processed. FIG.48 is a cross-sectional view of a switch array system illustrating theintegration and packaging of a MEMS switch array based chip-Lidar module4800.

MEMS structures can have multiple failing mechanisms (e.g., dust,moisture), therefore, all the components of the chip-Lidar need to bepackaged together and hermetically sealed. A hermetically sealed LIDARmodule 4800 includes a heat sink/substrate platform 4802, a light source4804 (e.g., laser, LED, or other commonly used light source), a lightcoupling component 4806, a photonic integrated circuit (PIC) chip withMEMS switch and ASIC control 4808, a lens 4810, an anti-reflective innercoating 4812, an anti-reflective outer coating 4814, one or more photodetector(s) 4816 (e.g., photo diode, photo transistor, charge coupledevice, or other commonly used photo detector), and other necessarycoupling components. The light source 4804 may be coherent andpolarized.

One example of system integration and packaging is shown in FIG. 48. Allthe components are integrated on one substrate platform with heatdissipation mechanisms, and hermetic sealed in one package. The cap ofthe package includes a window area which is transparent to thewavelength that is used in the LIDAR chip so that the light can emit outfrom the package and return back to the PIC chip. This window area cancover part or entire surface of the cap. Anti-reflection coatings on theinside and outside surface of the window can help reduce the reflectionwhen light transmit through the window. Different parts of the systemmay be packaged into different pressure levels and with differentcompositions of gas. For example, the MEMS switch array/PIC 4808 needs acertain pressure level (e.g., above 1 Torr) to induce damping so thatMEMS switches can stop at the position to turn on the switch. To reachthis purpose, heavy gases such as nitrogen, argon, etc. are used to fillthe chamber till the needed pressure level is reached. While other thanthis area (i.e., within the hermetically sealed module 4800), thepressure may be a vacuum pressure level (e.g., below 1 mTorr) tominimize the influence of particles and moisture. The hermeticallysealing temperature of 4800 should be lower than the temperaturethreshold levels that may affect the performance of the other components(e.g., PIC 4808, light source 4804, photo detector 4816) in the system.For example, the sealing temperature is recommended to stay below 300°C. so that the laser performance wouldn't be affected. Regarding theintegration of an ASIC, die bonding via silicon throughputs can minimizethe influence of electrical paths on the switching speed and switchingperformance.

This section proposes multiple designs and concepts of MEMS switch andits array for optical coupling. These proposed structures can be used inoptical terminals for optical beam steering. Here, different design andlayout arrangement methods for MEMS switch and MEMS switch array aredescribed. All these methods can be used in building optical beamsteering terminals.

One example of the MEMS switch array design is shown in FIG. 49. FIG. 49is a perspective view of a dual grating switch 4900 that travelstransversely 4906 with stop positions in-plane with waveguides 4912. Thesubstrate 4902 has multiple type I switches (e.g., 4910 a, 4910 b) tochannel light to bus waveguides 4912 a, 4912 b, 4912 c, and 4912 d. Inthis illustration, the dual grating 4914 a and 4914 b is either alignedsuch that grating 4914 a is aligned with a bus waveguide 4912 a, or suchthat grating 4914 b is aligned with bus waveguide 4912 b, such thatlight 4904 is coupled.

Here the gratings are used as optical coupler/antenna integrated withthe MEMS switch to illustrate the concept. Other optical coupler/antennadesigns also work for this concept. In the MEMS switch array shown inFIG. 49, each MEMS switch carries two optical antennas and is in chargeof two pixels on top of two adjacent bus waveguides. Each MEMS switchcan be actuated horizontally and move the two grating couplers/antennasalong x-direction across two waveguides. The MEMS switches have twopositions (4914 a and 4914 b): one grating overlaps with either one ofthe two waveguides (one pixel is ON, position 4914 a and position 4914b). For example, to turn on the second pixel above waveguide 4912 b, therow switch 4910 b is turned on, and the MEMS switch is actuated to movethe two grating couplers/antennas towards −x direction so that onegrating coupler/antenna can have enough overlap with waveguide 4912 band sufficient light can couple from waveguide 4912 b to that gratingand then emit to free space. Depending on which pixel will be turned on,the switch will be deflected until a certain stop against a mechanicalspring (as shown in the single switch sketch in FIG. 49). A comb-driveactuator can be used to actuate in-plane motion of the switch. Since thegrating is larger than the waveguide, back and forth bouncing will haveonly a very small influence on the performance. The deflection can bedone electrostatically, inductively, piezo-electrically or similar. Thedistance between the grating layer and the bus waveguide layer should besmall enough to make sure sufficient light can couple from bus waveguideto grating when the switch is at either position 4914 a or position 4914b. The advantage for this design is that the number of MEMS switch isonly half of the number of pixels.

Another design of the MEMS switch array is shown in FIG. 50, where theMEMS switches are also actuated to move horizontally along x-axis andone MEMS switch carry more than one optical couplers/antennas (hereagain grating is used as a coupler/antenna example to illustrate theconcept).

FIG. 50 is a perspective view of a dual grating switch 5000 that travelstransversely 5006 with stop positions in-plane and off-plane withwaveguides 5012. The substrate has multiple type I switches (e.g., 5010a, 5010 b) to channel light to bus waveguides 5012 a, 5012 b, 5012 c,and 5012 d. In this illustration, the dual grating 5014 a and 5014 b iseither aligned such that grating 5014 a is aligned with a bus waveguide5012 a, grating 5014 a and 5014 b is centered in between adjacent buswaveguides 5012 a and 5012 b such that no light is coupled, or such thatgrating 5014 b is aligned with bus waveguide 5012 b such that light iscoupled. These MEMS switches 5000 have three positions as shown in FIG.50: neutral position where two gratings are located between twowaveguides and no overlap with either of them (both pixels are OFF,position 5014), one grating overlaps with one waveguide (one pixel isON, position 1 and position 5014 a). Similarly, depending on which pixelwill be turned on, the switch will be deflected until a certain stopagainst a mechanical spring (as shown in the sketch with single switchin FIG. 50). Since the grating is larger than the waveguide, back andforth bouncing will have only a very small influence on the performance.The deflection can be done electrostatically, inductively,piezo-electrically or similar. In this design, however, the row switchesare not necessary because position 5014 is a complete OFF position(neither grating is overlapping with either of the bus waveguides). Thewaveguides can be connected by splitter trees, and by turning the switchto position 5014 a and 5014 b to switch on different pixels. In thiscase, this MEMS switch is a three-way switch. And of course, thedistance between the grating layer and the bus waveguide layer should besmall enough to make sure sufficient light can couple from bus waveguideto grating when the switch is at either position 5014 a or position 5014b.

FIG. 51 is a perspective view of a bimorphic switch 5100 in which agrating 5108 is an in-plane position. The bimorphic switch 5100 includesa substrate 5102 and suspended above the substrate 5102 is a grating5108 on a suspension layer 5104 having a bimorphic piezoelectricactuator 5106. When the bimorphic piezoelectric actuator 5106 isactivated 5110, the bimorphic switch 5100 moves to FIG. 52. FIG. 52 is aperspective view of a bimorphic switch 5200 that rotates a grating 5208vertically in an off-plane position. The biomorphic switch 5200 includesa substrate 5202 and suspended above the substrate 5202 is a grating5208 on a suspension layer 5204 having a bimorphic piezoelectricactuator 5206.

FIG. 53 is a perspective view of switch array 5300 in which gratingelements rotate about an axis perpendicular with the wave guide (e.g.,rotate about the x-axis). A substrate 5302 supports bus waveguides 5312such that light traveling in a direction 5310 can be distributed to eachbus waveguide 5312 a, 5312 b, 5312 c, and 5312 d. Here gratings 5316,5304, 5314 are configured to rotate 5306 about the x-axis and whenactive such as grating 5314, light 5308 is channeled from the buswaveguide 5312 b. Although this is shown as transmitting light, this canbe also be used to receive light. Similarly, FIG. 54 is a perspectiveview of switch array 5400 in which grating elements rotate about an axisparallel with the waveguide (e.g., rotate about the y-axis). A substrate5402 supports bus waveguides 5412 such that light traveling in adirection 5410 can be distributed to each bus waveguide 5412 a, 5412 b,5412 c, and 5412 d. Here gratings 5416, 5404, 5414 are configured torotate 5406 about the y-axis and when active such as grating 5414, light5408 is channeled from the bus waveguide 5412 b. Although this is shownas transmitting light, this can be also be used to receive light.

MEMS switches can also be designed to tilt or fold, as shown in FIG. 53and FIG. 54. In the design of FIG. 53, the MEMS switches are actuated torotate in the y-z plane around x-axis. When the MEMS switch is inparallel with y-axis, there's overlap between grating and bus waveguide,and if the distance between the grating and waveguide is kept smallenough, light can couple from bus waveguide to grating and further emitto free space, thus the MEMS switch is turned ON (FIG. 51). When theMEMS switch is tilted to a large enough angle that the light coupling isvery weak, the MEMS switch is OFF (FIG. 52). Similarly, as shown in FIG.54, the MEMS switches are actuated to rotate in the x-z plane aroundy-axis. The MEMS switch can be actuated by bimorph piezoelectricactuators as shown in FIG. 51 and FIG. 52 or electro active polymers.

The switches can also be rotated in-plane to slide over the waveguide(like a disc gyro), not only on a 90 degree angle. Similar to FIG. 55,but on a different scale. FIG. 55 is a top view of a grating array 5500on a rotary platter 5502 that utilizes a rotational mechanism to alignin-plane and off-plane operation. The rotary platter 5502 includesgratings 5504 arranged in an array such that rotation 5508 of theplatter allows gratings 5504 to align with bus waveguides 5506 totransmit or receive light. An advantage is that the antennas arecontrolled by one motor only instead of each antenna is controlled byone switch. The antennas can be designed to have a certain pattern thatthe polarization is not affected during rotation.

Further, the MEMS switchable gratings can use bi-stale membrane toreduce operation power. In this case, the MEMS switch actuation may be acombination of two methods to achieve its ON or OFF state. FIG. 56A is across sectional view of a coupler waveguide 5600 with a bi-stablemembrane 5612 in an OFF position. A substrate 5602 supports a buswaveguide 5604, an actuation electrode 5606, and a mechanical stop 5608.On a suspended layer is the bi-stable membrane 5612 that includes areaction electrode 5607, a mechanical stop 5608, and a coupler waveguide5610. FIG. 56B is a cross sectional view of a coupler waveguide with abi-stable membrane 5612 in an ON position. The switch, illustrated inFIG. 56A, has the coupler waveguide 5610 (with gratings) on a flexibleupper membrane 5612. In the OFF state, the coupler waveguide 5610 isseparated from the bus waveguide 5604. To change the switch to the ONstate, the coupler waveguide 5610 needs to be pulled down to the buswaveguide 5604 in FIG. 56B. An electrostatic pull-down force applied byelectrodes 5606 and 5607 is one actuation method, but this needsconstant current to keep the switch on. This would increase the powerneeded to operate the device. To eliminate the need to keep constantpower applied to keep the device on, a stress tuning of the membrane canbe implemented to create a bi-stable membrane. This would be done bydepositing a compressively stressed film 5612 to the top surface of themembrane coupler waveguide 5610. The stress needs to be tuned such thatthe membrane is either parallel or very slightly bowed up compared tothe lower surface. This membrane has bi-stable characteristics, meaningthat it can be flat or slightly bowed up, with no actuation force, andwhen pulled down with electrostatic actuation, stays down even when thepower applied by electrode 5606 and 5607 is stopped. This approachenables turning the switch on by using only a short power pulse to pullit down, and keeping the switch on by the bi-stable membrane itself, nopower is needed while the switch is in on state. To return the membraneto the separated off state, a pulsed repulsive electrostatic force isused to push the membrane to the separated off mode.

These proposed in-plane MEMS switches can also be organized in an arrayand combine with lens to do beam steering in optical transmitter,receiver, or transceiver terminals. All the switch combination andsplitter tree combination concepts and row/column wiring concepts alsowork with the proposed in-plane MEMS switches.

While all of the invention has been illustrated by a description ofvarious embodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the general inventive concept.

1. An optical switch comprising: a first bus waveguide supported by asubstrate; an optical antenna suspended over the first bus waveguide viaa spring; and interdigitated electrodes coupling the substrate withoptical antenna and configured to control a position of the opticalantenna relative to the first bus waveguide, wherein when a voltagedifference applied to the interdigitated electrodes is less than a lowerthreshold, the optical antenna is at a first position separated from thefirst bus waveguide by a first vertical distance, when the voltagedifference applied to the interdigitated electrodes is greater than anupper threshold, the optical antenna is at a second position separatedfrom the first bus waveguide by a second vertical distance less than thefirst vertical distance.
 2. The optical switch of claim 1 furthercomprising, a second bus waveguide supported by the substrate andparallel with the first bus wave guide, wherein when a voltagedifference applied to the interdigitated electrodes is less than a lowerthreshold, the optical antenna is at a first position a first distanceoffset from the first bus waveguide, when the voltage difference appliedto the interdigitated electrodes is greater than an upper threshold, theoptical antenna is at a second position a second distance offset fromthe second bus waveguide.
 3. The optical switch of claim 2, wherein afirst coupling efficiency between the first bus waveguide and theoptical antenna is greater than 50 percent and a second couplingefficiency between the second bus waveguide and the optical antenna isless than 1% when less than the lower threshold voltage difference isapplied to the interdigitated electrodes, and the first couplingefficiency between the first bus waveguide and the optical antenna isless than 1 percent and the second coupling efficiency between thesecond bus waveguide and the optical antenna is greater than 50 percentwhen greater than the upper threshold voltage difference is applied tothe interdigitated electrodes.
 4. The optical switch of claim 1, whereinthe lower threshold voltage difference is 5 Volts, and the upperthreshold voltage difference is 20 volts.
 5. The optical switch of claim1, wherein the substrate is a Silicon on Insulator (SoI) substrate andthe bus waveguide is etched in a silicon layer of the substrate that iscoupled with an insulating layer.
 6. The optical switch of claim 1arranged in an array of optical switches, wherein the optical antenna isan array of optical antennae arranged in at least two columns, the twocolumns being spaced apart at an interval, the array of optical antennaebeing arranged in at least one row such that the first position isseparated from the second position by the interval.
 7. The opticalswitch of claim 6 further including an optical tree configured todistribute light to the array of optical antennae, the optical tree isconfigured to selectively enable one of the at least one rows.
 8. Anoptical switch comprising: a bus waveguide supported by a substrate; anoptical antenna suspended over the bus waveguide via a spring; andinterdigitated electrodes coupling the substrate with optical antennaand configured to control a position of the optical antenna relative tothe bus waveguide, wherein when a voltage difference applied to theinterdigitated electrodes is less than a lower threshold, the opticalantenna is disposed at a first vertical position above the buswaveguide, when the voltage difference applied to the interdigitatedelectrodes is greater than an upper threshold, the optical antenna isdisposed at a second vertical position above the bus waveguide, and thefirst position is separated from the second position by a predetermineddistance.
 9. The optical switch of claim 8, wherein a couplingefficiency between the bus waveguide and the optical antenna is greaterthan 50 percent when the optical antenna is at the first position and atthe second position.
 10. The optical switch of claim 9 arranged in anarray of optical switches, wherein the optical antenna is an array ofoptical antennae arranged in at least two rows spaced apart at aninterval, and at least one column such that the first position isseparated by the second position by the interval.
 11. The optical switchof claim 10 further including an optical tree configured to distributelight to the array of optical antennae, wherein the array of opticalantennae is arranged in at least one row and at least one column and theoptical tree is configured to selectively enable one of the at least onerows.
 12. The optical switch of claim 10 further including an opticaltree configured to collect light from the array of optical antennae,wherein the array of optical antennae is arranged in at least two rowsand at least one column and the optical tree is configured toselectively enable one of the at least one rows.
 13. The optical switchof claim 10 further including a lens spaced apart from the substrate andconfigured to diffract light onto the optical antenna, wherein the lensis configured to translate along a vector perpendicular to thesubstrate, and a distance of the lens from the substrate changes as thelens translates along the vector.
 14. The optical switch of claim 10further including a lens spaced apart from the substrate and configuredto diffract light onto the optical antenna, wherein the substrate isconfigured to translate along a vector perpendicular to lens and adistance of the substrate from the lens changes as the substratetranslates along the vector.
 15. The optical switch of claim 10, whereinwhen a voltage difference applied to the interdigitated electrodes isbetween the lower threshold and the upper threshold, then the couplingefficiency is greater than 50 percent.
 16. A beam steering systemcomprising: a bus waveguide supported by a substrate; an optical antennasupported a distance over the bus waveguide via a spring; interdigitatedelectrodes that couple the substrate to the optical antenna and areconfigured to control a position of the optical antenna relative to thebus waveguide; an optical tree having at least one type of opticalswitch, the optical tree configured to collect light from the opticalantenna; and a lens spaced apart from the substrate and configured todiffract the light onto the optical antenna, wherein when a voltagedifference applied to the interdigitated electrodes is less than a lowerthreshold, the optical antenna is positioned a first distance offsetfrom the bus waveguide, when the voltage difference applied to theinterdigitated electrodes is greater than an upper threshold, theoptical antenna is positioned a second distance offset from the buswaveguide, and the second distance is less than the first distance. 17.The beam steering system of claim 16, wherein the optical antenna is anarray of optical antennae arranged in at least one row and at least onecolumn, and the optical tree is configured to selectively enable one ofthe at least one row.
 18. The beam steering system of claim 16, whereinthe optical antenna is an array of optical antennae arranged in at leastone row and at least one column, and the optical tree is configured toselectively enable one of the at least one column.
 19. The beam steeringsystem of claim 16, wherein the lens is configured to translate along avector perpendicular to the substrate and the distance of the lens fromthe substrate is changed as the lens translates along the vector. 20.The beam steering system of claim 19, wherein the optical antenna is atwo dimensional grating that provides a Gaussian beam spot in a farfield, and the Gaussian beam spot is focused on the optical antenna asthe lens translates along the vector.